In my quest for a swimming coach I found Swim121 near Chesterfield. The first problem was in locating it but that was due to my carelessness rather than any error in the company's location map. I was disappointed to find that the pool was only 10m long. As my major issue is fatigue it is hard to induce that in very short lengths. Also the pool lacks any internal markings so you have to keep quite a check on how many strokes you'v done per length to avoid hitting the end.
The teacher gave me some tips about my stroke, in particular that I probably wasn't exhaling sufficiently for the effort I was making. This was also linked to a rushed arm stroke that gives a short window for inspiration. Having said that, I didn't feel I'd settled into my stroke at all in the half hour due to the short pool length.
He also thought that I should adopt a thumb-first entry style to reduce air capture on hand entry which some online 'experts' feel is bad practice nowadays. Here's an example but there are others! This is probably trivia but anything with a risk of injury isn't ideal for a stiff 50 year old.